Tracking receiver with integrated phase calibration and method

ABSTRACT

A system and method of the disclosure relates to satellite tracking. The system may comprise a tracking receiver that includes a first analog-to-digital (A/D) converter coupled between a sum input and a digital signal processor (DSP), a second A/D converter coupled between a difference input and the DSP, and a calibration output coupled to the sum input and coupled to the difference input. The first A/D converter may convert an signal received at the sum input into a sum digital signal, and provide the sum digital signal to the DSP. The second A/D converter may convert an signal received at the difference input into a difference digital signal, and provide the difference digital signal to the DSP. The tracking receiver may generate an calibration signal and provide the calibration signal through the calibration output.

CROSS-REFERENCE TO RELATED APPLICATION

The present application for patent is a Continuation of U.S. patentapplication Ser. No. 16/209,737 filed Dec. 4, 2018, which claims thebenefit of U.S. Provisional Application No. 62/594,447, filed Dec. 4,2017, each of which are assigned to the assignee hereof, and expresslyincorporated by reference herein.

BACKGROUND Field

The present disclosure relates generally to a tracking system withintegrated phase calibration for use with a radio frequency directionalantenna assembly.

Background

Existing satellite tracking systems use a labor intensive phase matchingprocess between multiple radio frequency (if) paths. For example, rfcables are trimmed in length, and manual phase shifters are adjusted inthe field after deployment. Further, low-noise amplifiers used in the rfpaths must be matched to a reference.

In addition, long (and expensive) rf cables run alongside the antennafor providing tracking signals. The cables may be damaged in the field.

There is therefore a need for a technique for eliminating requirementsfor phase matched components, manual phase shifters/adjustments, orlabor intensive rf cable trimming.

SUMMARY

An aspect of the present disclosure may reside in a system for trackinga satellite. The system may comprise a tracking receiver including a suminput, a difference input, a digital signal processor (DSP), a firstanalog-to-digital (A/D) converter, and a second A/D converter. The firstA/D converter may be coupled between the sum input and the DSP. Thefirst A/D converter may be configured to convert a signal received atthe sum input into a sum digital signal, and to provide the sum digitalsignal to the DSP. The second A/D converter may be coupled between thedifference input and the DSP. The second A/D converter may be configuredto convert a signal received at the difference input into a differencedigital signal, and to provide the difference digital signal to the DSP.The calibration output may be coupled to the sum input and coupled tothe difference input. The tracking receiver may be configured togenerate a calibration signal and provide the calibration signal throughthe calibration output.

In more detailed aspects of the disclosure, the DSP may be configured togenerate a phase correction value based on the sum digital signal andthe difference digital signal resulting from the calibration signalcoupled to the sum input and coupled to the difference input. The DSPmay be further configured to store the phase correction value. The phasecorrection value may correspond to a phase difference between the sumdigital signal and the difference digital signal. A first calibrationsignal insertion component may be coupled between the calibration outputand the sum input, and may define a first signal path between the firstcalibration signal insertion component and the sum input. A secondcalibration signal insertion component may be coupled between thecalibration output and the difference input, and may define a secondsignal path between the second calibration signal insertion componentand the sum input. The first signal path and the second signal path mayhave different phase shifts. The DSP may be configured to generate aphase correction value based on a phase difference between the firstsignal path and the second signal path.

In other more detailed aspects of the disclosure, the first calibrationsignal insertion component may comprise a first coupler, and the secondcalibration signal insertion component may comprise a second coupler.The first coupler may have a first antenna signal input, a firstcalibration signal input, and a first coupled signal output. The firstcalibration signal input may be coupled to the calibration output, andthe first coupled signal output may be coupled to the sum input. Thesecond coupler may have a second antenna signal input, a secondcalibration signal input, and a second coupled signal output. The secondcalibration signal input may be coupled to the calibration output, andthe second coupled signal output may be coupled to the difference input.

A first amplifier may be coupled between the first coupled signal outputand the sum input, and a second amplifier may be coupled between thesecond coupled signal output and the difference input. Likewise, a firstmixer may be coupled between the first coupled signal output and the suminput, and a second mixer may be coupled between the second coupledsignal output and the difference input. A data antenna may be coupled tothe first antenna signal input and configured to generate a sum signal,and an offset antenna may be coupled to the second antenna signal inputand configured to generate a difference signal.

In other more detailed aspects of the disclosure, the first calibrationsignal insertion component may comprise a first switch, and the secondcalibration signal insertion component may comprise a second switch. Thefirst switch may have a first antenna signal input, a first calibrationsignal input, and a first switched signal output. The first calibrationsignal input may be coupled to the calibration output, and the firstswitched signal output may be coupled to the sum input. The secondswitch may have a second antenna signal input, a second calibrationsignal input, and a second switched signal output. The secondcalibration signal input may be coupled to the calibration output, andthe second switched signal output may be coupled to the differenceinput.

The system may further comprise an antenna assembly configured togenerate an antenna sum signal at a sum output, and an antennadifference signal at a difference output. The sum output may be coupledto the sum input, and the difference output may be coupled to thedifference input. The antenna assembly may include a TE21 coupler havingthe sum output and the difference output.

In other more detailed aspects of the disclosure, the DSP may beconfigured to generate a tracking signal for moving the antenna assemblyand to store a phase correction value generated using the calibrationsignal. The tracking signal may be generated based on the phasecorrection value, and a source signal received from a target satelliteusing the antenna assembly to generate the antenna sum signal and togenerate the antenna difference signal. The tracking receiver may beattached to the antenna assembly such that the tracking receiver moveswith the antenna assembly. The antenna assembly may have a feed assemblyand a reflector, and the tracking receiver may be housed within a can ofthe feed assembly.

The DSP may be further configured to store a second phase correctionvalue, The second phase correction value may be associated with a phasedifference between a first signal path through the antenna assembly tothe sum output and a second signal path through the antenna assembly tothe difference output.

Another aspect of the disclosure may reside in a phase calibrationmethod. In the method, a first calibration signal from an calibrationoutput of a tracking receiver may be received at a sum input of thetracking receiver, and a second calibration signal from the calibrationoutput may be received at a difference input of the tracking receiver.The first calibration signal may be converted into a sum digital signal,and the second calibration signal may be converted into a differencedigital signal. A phase correction value may be generated based on thesum digital signal and the difference digital signal.

In more detailed aspects, the sum input may be coupled to a sum outputof an antenna assembly, and the difference input may be coupled to adifference output of the antenna assembly. The phase correction valuemay be based on a phase difference between a first path from the sumoutput to the sum input and a second path from the difference output andthe difference input. A tracking signal may be generated based on thephase correction value, and a source signal received from a targetsatellite using a data antenna to generate an antenna sum signal and anoffset antenna to generate an antenna difference signal

As one example, the antenna assembly may include the data antenna thatmay generate a sum signal at the sum output, and may include the offsetantenna that may generate a difference signal at the difference output.Alternatively, the antenna assembly may include a TE21 coupler that maygenerate the sum signal at the sum output and the difference signal atthe difference output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a satellite tracking systemhaving a tracking receiver.

FIG. 2 is a schematic diagram of an example of a satellite trackingsystem having an antenna assembly with an integrated tracking receiver.

FIG. 3 is a block diagram of an example of switches for coupling acalibration signal.

FIG. 4 is a block diagram of an example of a tracking receiver thatprovides a calibration signal.

FIG. 5 is a schematic diagram of an example of an antenna assemblyhaving a data antenna and offset antennas.

FIG. 6 is a schematic diagram of an example of an external source forcalibrating a phase shift of an antenna assembly.

FIG. 7 is a flow diagram of an example of a method for phase calibrationin a tracking receiver.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, a tracking system 10 may have anantenna assembly 20 and a tracking assembly 30 for tracking a satellite40 (or similar space traveling object) in order to receive signals fromthe satellite 40 and to transmit signals to the satellite. The trackingmay be performed by receiving signals in the S-band, X-band, Ka-band,and similar signal bands. The antenna assembly 20 may be ground mountedand may include a parabolic reflector 50 having, as an example, adiameter from about 5 meters to about 13 meters. The antenna assembly 20may provide a sum signal and a difference signal for use in thetracking.

The tracking system 10 may require calibration of phase differences inthe signal paths of the sum and difference signals through the antennaassembly 20 and the tracking assembly 30. Initial phase calibration maybe performed in connection with the installation and setup of thetracking system 10. For example, a phase offset calibration of theantenna assembly 20 may be performed by a one-time calibration performedwithout the parabolic reflector 50, at a mid-range temperature.

The antenna assembly 20 may be coupled to the tracking assembly 30 at ornear calibration signal insertion components, 190 and 200. The phaseoffset (or phase difference) of the signal paths/channels in thetracking assembly 30 may be determined by a tracking receiver 110 usinginserted calibration signals. The tracking receiver 110 may have atracking mode of operation and a calibration mode of operation. Thetracking assembly 30 may have aspects that support the calibration mode.

As an example, the tracking receiver 110 may include a sum input 120, adifference input 130, a first analog-to-digital (A/D) converter 140, asecond A/D converter 150, a digital signal processor (DSP) 160, andcalibration output 170. The first A/D converter 140 may be coupledbetween the sum input 120 and the DSP 160. The first A/D converter 140may be configured to convert a signal received at the sum input 120 intoa sum digital signal, and to provide the sum digital signal to the DSP160. The second A/D converter 150 may be coupled between the differenceinput 130 and the DSP 160. The second A/D converter 150 may beconfigured to convert a signal received at the difference input 130 intoa difference digital signal, and to provide the difference digitalsignal to the DSP 160. The calibration output 170 may be coupled to thesum input 120 and coupled to the difference input 130. The trackingreceiver 110 may be configured to generate a calibration signal andprovide the calibration signal through the calibration output 170. Anoutput splitter 180 may split the calibration signal.

In more detailed aspects of the disclosure, the DSP 160 may beconfigured to generate a phase correction value PC1 based on the sumdigital signal and the difference digital signal resulting from thecalibration signal coupled to the sum input 120 and coupled to thedifference input 130. The DSP 160 may be further configured to store thephase correction value. The phase correction value may correspond to aphase difference between the sum digital signal and the differencedigital signal. A first calibration signal insertion component 190 maybe coupled between the calibration output 170 and the sum input 120, andmay define a first signal path between the sum input 120 and the firstcalibration signal insertion component 190. A second calibration signalinsertion component 200 may be coupled between the calibration output170 and the difference input 130, and may define a second signal pathbetween the difference input 130 and the second calibration signalinsertion component 200. The first signal path and the second signalpath may have different phase shifts due to one or more components alongthe respective signal paths. The DSP 160 may be configured to generate aphase correction value (e.g., PC1) based on a phase difference betweenthe first signal path and the second signal path in response to thecalibration signal.

In the illustrated example, the first calibration signal insertioncomponent 190 may comprise a first coupler 210, and the secondcalibration signal insertion component 200 may comprise a second coupler220. The first coupler 210 may have a first antenna signal input 230, afirst calibration signal input 240, and a first coupled signal output250. The first calibration signal input 240 may be coupled to thecalibration output 170, and the first coupled signal output may becoupled to the sum input 120. The second coupler 220 may have a secondantenna signal input 260, a second calibration signal input 280, and asecond coupled signal output 290. The second calibration signal input260 may be coupled to the calibration output 170, and the second coupledsignal output 290 may be coupled to the difference input 130. The firstcoupler 210 and the second coupler 220 may be directional couplers.

A first amplifier 300 may be coupled between the first coupled signaloutput 250 and the sum input 120, and a second amplifier 310 may becoupled between the second coupled signal output 290 and the differenceinput 130. Likewise, a first mixer 320 may be coupled between the firstcoupled signal output 250 and the sum input 120, and a second mixer 330may be coupled between the second coupled signal output 290 and thedifference input 130.

In the illustrated example, the antenna assembly 20 includes a dataantenna 340 and one or more offset antennas 350. Alternatively, theantenna assembly 20 may be different. The antenna assembly 20 may becoupled to the first antenna signal input 230 and may generate a sumsignal. A splitter 345 may split the signal from the data antenna 340 toprovide a data signal DATA. The antenna assembly 20 may be coupled tothe second antenna signal input 260 and may generate a differencesignal.

With further reference to FIG. 3, in another example, the firstcalibration signal insertion component 190 may comprise a first switch370, and the second calibration signal insertion component 200 maycomprise a second switch 380. The first switch 370 may have a firstantenna signal input 230′, a first calibration signal input 240′, and afirst switched signal output 250′. The first calibration signal input240′ may be coupled to the calibration output 170, and the firstswitched signal output 250′ may be coupled to the sum input 120. Thesecond switch 380 may have a second antenna signal input 260′, a secondcalibration signal input 280′, and a second switched signal output 290′.The second calibration signal input 260′ may be coupled to thecalibration output 170, and the second switched signal output 290′ maybe coupled to the difference input 130.

With reference to FIG. 4, the calibration signal may be generated by theDSP 160 using a configurable direct digital synthesizer (DDS) 410. TheDDS 410 outputs a digital calibration signal to a digital-to-analogconverter (DAC) 420. The DAC 420 outputs the calibration signal, at thecalibration output 170, based on the digital calibration signal. Thiscalibration signal may also be generated with a phase-locked-loop (PLL)and a voltage-controlled oscillator (VCO) (not shown). Two voltagecontrolled amplifiers, 430 and 440, may set the level of the signalinput into the A/D converters, 140 and 150, respectively. A differentialphase detector 450 detects the phase difference (or phase offset)between the digital sum signal and the digital difference signal outputby the A/D converters, 140 and 150, respectively, The differential phasedetector 450 generates the phase correction value based on the detectedphase difference and provides the phase correction value to a phaseadjustment rotator 460. In the illustrated example, the phase adjustmentrotator 460 digitally adjusts the phase of the digital difference signalin this example. More generally, the phase of the digital sum signaland/or the phase of the digital different signal may be adjusted usingthe phase correction value in order to phase match (or phase align) thetwo signals. The adjusted digital difference signal is combined with thedigital sum signal by a combination/sum operation 470.

In a more detailed aspect of the disclosure, the differential phasedetector 450 may use a complex conjugate multiply, and a complexintegrate and dump. An instantaneous estimate of the phase offset may becalculated using the complex conjugate multiply. The sum signal may bemodeled by e^((jωt+θ) ¹ ⁾ and the difference signal may be modeled bye^((jωt+θ) ² ⁾. A complex conjugate multiply may produce the following:CC_(instant)=e^((jωt+θ) ¹ ⁾*e^(−1*(jωt+θ) ² ⁾=e^((jωt+θ) ¹ ^()−jωt−θ) ²⁾=e^((θ) ¹ ^(−θ) ² ⁾=cos(θ₁−θ₂)−j sin(θ₁−θ₂). This instantaneous phaseestimate may be averaged using a complex integrate and dump. The valuesmay be accumulated over 2^(N) samples, and the accumulated result may bedivided by 2^(N): CC_(ave)=(½^(N))Σ[cos(θ₁−θ₂)−j sin(θ₁−θ₂)]. Theaveraged complex result may be input into an arctan function to recoverthe phase offset value:Θ_(ave)=arctan[Im(CC_(ave))/Re(CC_(ave))]≈−(θ₁−θ₂).

The phase adjustment rotator 460 may phase rotate the digital differencesignal to remove the phase offset between the sum and differencesignals. The rotator 460 receives the difference digital signal and theresulting phase offset value, and outputs a phase rotated complex value.

In some embodiments, the phase calibration may be performed at multiplefrequencies within the operating bandwidth of the tracking system bygenerating CW tones at each step, and performing the phase errorcalibration at each of the steps. The steps may for example be selectedto correspond to a predetermined maximum value (e.g., about 20 degreesof phase difference in a worst case scenario) of phase mismatch. Thus,the steps may be selected to allow for easy interpolation between steps.

The tracking receiver 30, integrated with the feed assembly 390, mayperform the phase matching of the radio frequency (rf) signal paths inthe digital domain of the DSP 160 using injection of the calibrationsignal into the signal paths. The tracking receiver 30 may be placedinside a feed can of the feed assembly 390, and may send and receive thecalibration signals to perform the phase calibration. During thetracking mode, the tracking receiver 30 also may output a tracking errorsignal to an Antenna Controller Unit (ACU) (not shown) via digitalsignals (e.g. Ethernet messages) rather than via an analog signal overexpensive rf cables.

These aspects allow for reduced cost in the components of the system.Phase matched low-noise amplifiers (LNAs) are no longer required, thusallowing the use of lower cost low-noise blocks (LNBs). Az/El switchcontrol and ACU functionality may be moved into the tracking receiver 30thus requiring less cabling between the ACU and the tracking receiver30. ACU functionality also may be moved to the tracking receiver, i.e.,bin integration. Using the calibration to align and combine the sum anddifference signals in the DSP 160 of the tracking receiver 30 providesmultiple benefits. As examples, it may eliminate an externalphaseshifter and coupler by creating a phaseshifter and coupler in theDSP 160. Further, it may reduce labor cost in construction of thetracking system 10. Delay and phase may be characterized, but matchingmay not be required between the sum and difference channels. It is mucheasier to characterize or measure phase than it is to physically cutcables to match phase.

The antenna assembly 20 can vary from embodiment to embodiment and maybe configured to generate an antenna sum signal at a sum output 400, andan antenna difference signal at a difference output 410. The sum outputmay be coupled to the sum input 120, and the difference output may becoupled to the difference input 130. In the example of FIG. 1, theantenna sum signal is generated by data antenna 340 and the antennadifference signal is generated by one or more offset antennas 350coupled to switch 360. As an alternative example, the antenna assembly20 may include a TE21 coupler having the sum output 400 and thedifference output 410.

With further reference to FIG. 2, the antenna assembly 20 may have afeed assembly 390 and a reflector 50, and the tracking assembly 30 maybe housed within a can of the feed assembly 390. The DSP 160 may beconfigured to generate a tracking signal for moving the antenna assembly20, and to store a phase correction value generated using thecalibration signal. The tracking assembly 30 may be attached to the feedassembly 390 such that the tracking assembly 30 moves with the antennaassembly 20. During a tracking mode of operation, the tracking signalmay be generated based on a stored phase correction value (e.g., PC1),and a source signal received from a target satellite 40 using theantenna assembly 20 to generate an antenna sum signal and to generate anantenna difference signal.

With reference to FIG. 5, the data antenna 540 may be a central feedhorn, and four surrounding offset antennas 550-N may be smaller feedhorns. Two of the offset antennas, 550-1 and 550-2, may be used forelevation tracking and may be positioned above and below the dataantenna 540. Two of the offset antennas, 550-3 and 550-4, may be usedfor horizontal (azimuth) tracking, and may be positioned to the rightand the left the data antenna 540. During calibration, a switch 360 maytime multiplex the offset antennas 550-N such that one offset antenna ata time is connected to the second antenna signal input 260.

The data antenna 540 may be aligned to the antenna boresite while theoffset antennas 550-N may be offset from boresite by a slight angle. Thedata antenna 540 may be used for acquiring data from the satellite 40(or other signal source) since it has the greatest sensitivity. The sumsignal from the data antenna 540 may be used to normalize the differencesignals from the offset antennas 550-N in order to keep a constant errorslope when a range to the satellite 40 is varying. The variation insignal due to range is common to all antennas so normalizing thedifference signals to the sum signal keeps the difference path errorslope constant. The signals from offset antennas 550-N are used togenerate the tracking signals.

The initial calibration of the phase shift (or phase offset or delay)for the signal paths through the antenna assembly 200 may be done onetime at in an indoor feed chamber (not shown). In one example, themeasurement may be made at room temperature, and the amount of phasechange over temperature may be estimated. This calibration may notinclude the reflector 50 and may need a correction for geometry effectssuch as parallax. The calibration may be able to align all of thedifference paths of the offset antennas 550-N, but it may not be able toalign with the sum path of the data antenna 340 because of differentpath lengths between the data antenna and the offset antennas.

The DSP 160 may be further configured to store another phase correctionvalue PC2. This phase correction value may be associated with a phasedifference between a first signal path through the antenna assembly 20to the sum output 400 and a second signal path through the antennaassembly 30 to the difference output 410.

With reference to FIG. 6, a boresite calibration may be performed tocalibrate the antenna assembly 20. No parallax correction is required inthis example since the calibration is being performed in the far-field.The source may be a boresite tower 610 having a microwave source 620 andgps accurate 10 MHz reference 630.

The reflector 430 may be included in the calibration. The antennaassembly 20 may be positioned or pointed offset from the boresight torevolve phase ambiguities and to give an adequate signal for the subjectdifference channel. Note that the temperature may not be in the centerof the temperature range because it may take place outdoors.Alternately, the source may be a satellite 40. Note that the calibrationtime may impact the data path when the antenna assembly 20 is off ofboresight.

The phase calibration of the tracking receiver 30 may be closed loop,and may determine a phase shift between the signal paths between, forexample, the couplers, 210 and 220, and the A/D converters, 140 and 150,respectively. The calibration may require the tracking receiver 30 to betaken offline. If a new LNA is installed in the field, the closed-loopcalibration may be performed to calibrate the new phase shift.

During tracking mode, the manner in which processing is performed by theDSP can be different for different types of feeds. In an antennaassembly 20 having a TE21 coupler, the phase states are 0, 90, 180, 270.There is no switching as the Azumith/Elevation separation is done byTE21 quadrature orthogonality between the Az/El. For linear polarizationwith a rotating feed, a coordinate transformation between Az/El of feedand Az/El of servo system is performed. For monoscan, the phase statesare 0, 180. Switching between Az and El paths is preformed by two switchinput, and phase matching to 180 deg hybrid in Az or El is used. ForEScan, the signal is amplitude only but the sum and diff signals arephase aligned. The switching is between four antennas based on fourswitch inputs.

With reference to FIG. 7, another aspect of the disclosure may reside ina phase calibration method 700. In the method 700, a first calibrationsignal from an calibration output of a tracking receiver 30 may bereceived at a sum input 120 of the tracking receiver 30, and a secondcalibration signal from the calibration output may be received at adifference input 130 of the tracking receiver. The first calibrationsignal may be converted into a sum digital signal, and the secondcalibration signal may be converted into a difference digital signal. Aphase correction value may be generated based on the sum digital signaland the difference digital signal.

In more detailed aspects, the sum input 120 may be coupled to a sumoutput 400 of an antenna assembly 20, and the difference input 130 maybe coupled to a difference output 410 of the antenna assembly 20. Thephase correction value may be based on a phase difference between afirst signal path from the sum output 400 to the sum input 120 and asecond signal path from the difference output 410 and the differenceinput 130 resulting from the calibration signal. A tracking signal maybe generated based on the phase correction value, and a source signalreceived from a target satellite 40 (or other signal source) by theantenna assembly 20 to generate an antenna sum signal an antennadifference signal.

As one example, the antenna assembly 20 may include the data antenna 340that may generate an antenna sum signal at the sum output 400, and mayinclude the offset antenna 350 that may generate an antenna differencesignal at the difference output 410. As another example, the antennaassembly 20 may include a TE21 coupler that may generate the antenna sumsignal at the sum output 400 and the antenna difference signal at thedifference output 410.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software as a computer program product, the functionsmay be stored on or transmitted over as one or more instructions or codeon a computer-readable medium. The code may be executed by the processorof the computer. Computer-readable media includes both non-transitorycomputer-readable storage media and communication media including anymedium that facilitates transfer of a computer program from one place toanother. A storage media may be any available media that can be accessedby a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if the software is transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, includes compactdisc (CD), laser disc, optical disc, digital versatile disc (DVD),floppy disk and blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A system for tracking a satellite, comprising: atracking receiver, including: a sum input; a difference input; a digitalsignal processor (DSP); a first analog-to-digital (A/D) convertercoupled between the sum input and the DSP, wherein the first A/Dconverter is configured to convert a signal received at the sum inputinto a sum digital signal, and to provide the sum digital signal to theDSP; a second A/D converter coupled between the difference input and theDSP, wherein the second A/D converter is configured to convert a signalreceived at the difference input into a difference digital signal, andto provide the difference digital signal to the DSP; and a calibrationoutput coupled to the sum input and the difference input, thecalibration output configured to output a calibration signal, whereinthe DSP is configured to receive the calibration signal at a firstfrequency of an operating bandwidth of the tracking receiver andgenerate a phase offset value for calibrating the tracking receiver at asecond frequency based on the calibration signal received at the firstfrequency.
 2. The system of claim 1, wherein the DSP is configured to:generate the phase offset value based on the sum digital signal and thedifference digital signal resulting from the calibration signal at thefirst frequency.
 3. The system of claim 2, wherein the calibrationoutput is configured to output the calibration signal at a plurality offrequencies of the operating bandwidth.
 4. The system of claim 3,wherein the DSP is configured to receive the calibration signal at eachfrequency of the plurality of frequencies and to interpolate between twoor more phase offset values to obtain the phase offset value forcalibrating the tracking receiver at the second frequency.
 5. The systemof claim 1, wherein the DSP is configured to: generate a phasecorrection value based on the sum digital signal and the differencedigital signal resulting from the calibration signal coupled to the suminput and coupled to the difference input; and store the phasecorrection value.
 6. The system of claim 5, wherein the phase correctionvalue corresponds to a phase difference between the sum digital signaland the difference digital signal.
 7. The system of claim 1, wherein thetracking receiver is configured to generate the phase offset value basedat least in part on a temperature of the tracking receiver.
 8. Thesystem of claim 1, further comprising: a first calibration signalinsertion component coupled between the calibration output and the suminput, and defining a first signal path between the first calibrationsignal insertion component and the sum input; and a second calibrationsignal insertion component coupled between the calibration output andthe difference input, and defining a second signal path between thesecond calibration signal insertion component and the sum input.
 9. Thesystem of claim 8, wherein the first signal path and the second signalpath have different phase shifts.
 10. The system of claim 8, wherein theDSP is configured to generate a phase correction value based on a phasedifference between the first signal path and the second signal path. 11.The system of claim 8, further comprising: a first amplifier along thefirst signal path; and a second amplifier along the second signal path.12. The system of claim 8, further comprising: a first mixer along thefirst signal path; and a second mixer along the second signal path. 13.The system of claim 8, wherein: the first calibration signal insertioncomponent comprises a first coupler having a first antenna signal input,a first calibration signal input, and a first coupled signal output,wherein the first calibration signal input is coupled to the calibrationoutput, and the first coupled signal output is coupled to the sum input;and the second calibration signal insertion component comprises a secondcoupler having a second antenna signal input, a second calibrationsignal input, and a second coupled signal output, wherein the secondcalibration signal input is coupled to the calibration output, and thesecond coupled signal output is coupled to the difference input.
 14. Thesystem of claim 13, further comprising: a data antenna coupled to thefirst antenna signal input and configured to generate a sum signal; andan offset antenna coupled to the second antenna signal input andconfigured to generate a difference signal.
 15. The system of claim 1,further comprising: an antenna assembly configured to generate anantenna sum signal at a sum output, and an antenna difference signal ata difference output, wherein the sum output is coupled to the sum input,and the difference output is coupled to the difference input.
 16. Thesystem of claim 15, wherein the antenna assembly incudes a couplerhaving the sum output and the difference output.
 17. A method,comprising: receiving, at a sum input of a tracking receiver, a firstcalibration signal at a first frequency of an operating bandwidth of thetracking receiver from a calibration output of the tracking receiver;receiving, at a difference input of the tracking receiver, a secondcalibration signal at the first frequency from the calibration output;converting the first calibration signal into a sum digital signal;converting the second calibration signal into a difference digitalsignal; and generating a phase offset value for calibrating the trackingreceiver at a second frequency based on the sum digital signal and thedifference digital signal.
 18. The method of claim 17, wherein thecalibration output is configured to output the first calibration signaland the second calibration signal at a plurality of frequencies of theoperating bandwidth.
 19. The method of claim 18, further comprising:receiving the first calibration signal and the second calibration signalat each frequency of the plurality of frequencies and to interpolatebetween two or more phase offset values to obtain the phase offset valuefor calibrating the tracking receiver at the second frequency.
 20. Themethod of claim 17, wherein the phase offset value is based at least inpart on a temperature of the tracking receiver.
 21. The method of claim17, further comprising: generating a tracking signal based on the phaseoffset value, and a source signal received from a target satellite usingan antenna assembly to generate an antenna sum signal and an antennadifference signal.
 22. The method of claim 21, wherein the trackingreceiver is attached to the antenna assembly such that the trackingreceiver moves with the antenna assembly in response to the trackingsignal.